1. Field of the Invention
The present invention relates to flame detectors, and more particularly to a flame detector resistant to false alarms.
2. Description of the Prior Art
It is well known to detect the presence of a flame due to the ultraviolet radiation which will occur sporadically from the flame. In the prior art, it is known to detect ultraviolet (UV) radiation by systems using gas discharge type electronic tubes. Typical of such systems is the flame detection system available from Detector Electronics Corporation which uses an ultraviolet sensor tube. Certain aspects of this system are disclosed in U.S. Pat. No. 3,952,196 to Larson.
One of the principal problems with known ultraviolet flame detecting systems is that of false alarms. There will normally be background strikes of ultraviolet energy or other radiation which may trigger a gas discharge type detector tube. Flames will produce groups of short bursts of ultraviolet radiation and most systems will not discriminate between such bursts and background counts, particularly if such systems are set to a sensitive threshold.
This problem is particularly acute in systems using hydrogen or other gases which burn with an essentially invisible flame. For example, at launch facilities for rockets, space vehicles and the like, flame detecting apparatus will automatically trigger fire extinguishing systems when a hydrogen flame is detected to prevent serious explosions from occurring. Thus, when a false alarm is interpreted as a flame, large amounts of extinguishing chemicals may be dumped at great expense.
There is a need for a sensitive flame detector system which can effectively discriminate between background ultraviolet radiation and radiation due to an actual flame.